U.S. Pat. No. 4,080,374 to Corn discloses that during hydrocyanation of pentenenitrile to adiponitrile some zero-valent nickel catalyst is oxidized to nickel cyanide which forms insoluble complexes with triarylborane. These insoluble complexes (solid catalyst degradation precipitate) become encrusted on the equipment surfaces, and lead to inefficient operation by loss of heat transfer capability and restriction of flow through the equipment. Some of the solid catalyst degradation precipitate remains suspended in the product fluid and interferes with efficient recovery of the zero-valent nickel catalyst by liquid/liquid extraction from the product fluid.